Automatic electric motor control system



April 27, 1948. G. E. VAN vEssEM 2,440,352

AUTOKATIC ELECTRIC MOTOR CONTROL SYSTEM Filed June'2, 1943 INVENTOR. 6mm VAN VESSEM Patented Apr. 27, 1948 AUTOMATIC ELECTRIC MOTOR CONTROL SYSTEM George E. Van Vessem, Naugatuck, Conn., as-

signor to The Bristol Company, Waterbury, Conn., a corporation of Connecticut Application June 2,1943, Serial No. 489,346

12 Claims. 1

This invention relates to control devices, and more especially to an automatic proportioning control, in which a floating control member is caused to assume a position more or less determined by the position of a measuring element quantitatively responsive to a condition subject to the effect of a medium regulated by said member.

In the automatic control of variables such as temperature, it is customary to provide a valve through which may flow a supply of fuel or other temperature aifecting agent, and to operate said valve by means of an electric motor whose action is commanded by a relay system subject to the deviation of the position of said valve from a position established by the mechanism of a temperature-sensitive instrument. One common method by which a proportional relationship may be established between the position oi the valve and that determined by the instrument is found in the combination of a slide-wire resistance adjustable in response to changes in the position of the valve, and another slide-wire resistance adjustable by action of the measuring instrument. These resistances being connected to form a bridge network with a sensitive detector in the bridge arm and a source of electrical energy suitably connected to the network, there is provided a simple means by which a motor actuated by said detector may be caused to operate the valve to a definite position determined by the setting of the slide-wire associated with the measuring instrument. This is a con- Ventional and well-known form of remote control, and is found in many devices for distant regulation of motors. Probably one of the earliest examples is that disclosed in U. S. Letters Patent No. 599,903 to M. Pfatischer, May 12, 1896. In the disclosure of Pfatischer, the principie is shown in its application to the remote operation of steering gear for ships, the rudder mechanism being mechanically attached to a suitably tapped rheostat, and the manually actuated control element on the bridge of the ship being attached to a similar rheostat, and a detecting relay connected between the two moving contactors, being arranged to control the performance of a steering engine or electric motor.

In the application of the slide-wire principle to the proportional control, for example, of a valve for regulating the temperature of an enclosed space containing materials to be processed, there enters the feature of time lag, which is inseparable from automatic control, and which tends to introduce a certain degree of overshooting" in the values of temperature attained. Coupled with this characteristic is the feature that a relay sufficiently rugged to effect control of a valve motor is likely to have a degree of sensitivity too low to utilize the full advantage obtainable from the electrical coupling between the controlling and controlled members.

It is an object of this invention to provide means whereby the sensitivity of a bridge coupling between a measuring instrument of the self-balancing type and a controlling valve or the like may be made as high as that of the detector in the measuring system of the selfbalancing instrument.

It is a further object to provide a form of "anticipatory control, in which the features of thermostatic regulation and proportioning control are combined to approximate closely an ideal straight-line characteristic.

It is a further object to provide means of the above nature in which the element of backlash due to 10st motion in mechanical parts or to coarseness of tapping in the bridge rheostats may be eliminated from the performance'of the mechanism.

The single figure of the drawings is a diagrammatic representation of an electrical temperature control system embodying the principles of the invention, and subject to actuation by a self-balancing pyrometer of the potentiometric type.

Referring now to the drawings:

The numeral l0 designates a furnace, oven, or other enclosed space adapted to be heated by the combustion of fluid fuel admitted thereto through a burner ii, and in which it is desired to maintain a predetermined constant temperature as determined by a thermocouple i2 located within the furnace, the regulation of said temperature being efiected by control of the position of a valve 53 connected in a conduit M through which said fuel is supplied to the burner it from a source it. The valve 13 is actuated by an operating mechanism it comprising a link member ll connected to a crank element l8 carried by a shaft it adapted for rotation through a limited angle by means of a reversible electric motor 20. The motor 20 is provided with opposed (field) windings 2i and 22, and a single (armature) winding 23, and is adapted for rotation in a direction depending upon which of the respective field windings is energized concurrently with the single armature winding. One end of each of the three motor windings is connected to a common conductor 24, the free ends of the field windings 2i and 22 to terminals 25 and 25 respectively, and the free end of the armature winding 23 to a terminal 27.

Potentiometer circuit and balancing mechanism The numeral 29 designates a self-balancing circuit mechanism similar to that fully set forth and disclosedin the Patent to F. B. Bristol, No. 2,320,066, issued May 25, 1943, and having the following structure: A galvanometer 8d of the conventional form includes a coil 3i freely pivoted between poles N and S of a permanent magaccents net or the equivalent. Electrical connection is made to the coil 3! by means of resilient leads or springs 32 and 33 connected respectively to conductors 34 and 35, forming elements in an electrical network hereinafter to be described, whereby upon passage of current from one to the other of said conductors through said galvanometer coil, the latter will tend to be rotated through a limited angle about its axis in a sense either clockwise or counter-clockwise, according to the direction of the current. Carried by the galvanometer coil is a pointer 36 bearing upon its extremity a, contact member 31 adapted to engage either of two stationary contacts 38 and 39, according to the sense of the deflection. The end of the coil 3i which is connected to the spring 33 is also connected to the pointer 38 by means of a conductor 40, whereby current may pass between the conductor 34 and the pointer 36 by flowing through the galvanometer coil 3!.

A potentiometer circuit includes a uniform slide-wire M of arcuate curvature extended between terminals 42 and 43 and supplied with a steady current from a battery 44, whose output may be regulated by means of an adjustable rheostat 45. Suitably engaging the slide-wire M is a movable contact-arm 43 fixed to a shaft 41 coaxial with the center of curvature of the slide wire 4|, and insulated therefrom, whereby upon rotation of said shaft through a limited angle, the contact arm 46 may traverse said slide wire through its length, and may assume any position along said slide wire, according to the angular position at which the shaft is brought to rest. An index 48, carried by the shaft 41, and cooperating with a fixed arcuate calibrated scale 49, provides an indication of the position of said contact arm 46 with respect to the slide-wire 4i.

Rotation of the shaft 41 for the purpose of shifting the contact arm 46 along the slide-wire 4| is effected by means of a reversible electric motor 50 having two opposed windings 5i and 52, adapted normally to be simultaneously energized and to maintain said motor stationary, and, when individually deenergized to operate said motor in either direction according to which of said windings remains energized. The shaft of the motor 50 carries a pinion 53 meshing with a gear 54 fixed to the shaft 41, whereby said shaft and elements carried thereby will be angularly moved according to which of the two windings of the motor 59 may be energized.

The potentiometer circuit comprising the slidewire 46, the battery 44, the rheostat 45, and the contact arm 46 is applied to the measurement of the thennoelectromotive force developed by the couple i2, and hence of the temperature within the enclosed space it. One element of the thermocouple is connected by means of a. conductor 55 to the terminal 42 of the slide wire, and the other element to the conductor 34 leading to one side of the galvanometer coil 3!. The conductor 35 leading to the other side of the galvanometer is flexibly or slidahly connected to the contact arm 36, whereby the potential at any point along said slide-wire due to the flow of current therethrough from the battery 44, may be applied to the conductor 35 according to the deflected position of the contact arm.

According to well known principles upon which the slide-wire are suitably adjusted. the position of the contact arm 48, and therefore of the index 48, corresponding to a balance of the potentiometer network, as indicated by a zero deflection of the galvanometer pointer 36, is a measure of the temperature to which the thermocouple i2 is exposed. The polarity of the thermocouple H, as connected to the conductors 34 and 35, is made such that upon an increase of potential developed by said couple due to an increase in the temperature to which it is exposed, the unbalance current due to the excess of said E. M. F. over that derived from the slide wire will cause to pass through the galvanometer coil 3| a current tending to swing said coil in a counter-clockwise sense, and cause the contact 31 carried by the pointer 36 to. be brought into electrical engagement with the stationary contact 38. In a similar manner a de-' crease in temperature at the thermocouple will cause the galvanometer coil to be deflected in an opposite sense, and the contact 3! brought into engagement with the stationary contact 39. The setting of the contact arm 46 with respect to the slide wire 4! is effected by the motor 50 through the medium of a relay combination of the type set forth in said F. B. Bristol patent and, while such combination will be briefly described, no invention thereof is. herein claimed.

A relay 64 embodies an actuating magnet coil 65 and an armature 66 subject thereto. Normally engaged contacts 67 and 68 are adapted to be separated by the movement of the armature transmitted through an insulating pad 69 when the coil 65 .is energized. Further contacts 10 and ii, also normally engaged, are adapted to be separated by movement of said armature transmitted through an insulating pad 72 when the coil 65 is energized. The coil 85 is fitted with a short circuited lag-plate or shroud i3; and, as fully set forth in said F. B. Bristol patent, said shroud and the physical dimensions and adjustments of the contact-actuating elements are so coordinated as to introduce a desirable timerelationship in the operation of the contacts.

A relay '84, similar in all respects to relay 64, embodies a magnet coil 75 and an armature it, together with normally closed contacts Ti and i3 actuated by said armature through an insulating pad 119, and further normally closed contacts and 8i actuated through an insulating pad $2. The coil 15 is lagged in a manner similar to the coil 85, and all the elements of the relay it are proportioned and adjusted to give a performance substantially identical with that of the relay 64 with respect to sequential actuation of contact elements. In addition to the contact elements thus far set forth as incorporated in the relay it, the contact 83 is made double acti and there is provided contact element 83 adapted to be engaged by said contact it when the latter is separated'irom engagement with the contact H by action. of the armature it in response to energization of the relay coil '65. 'This feature is not disclosed in said ,F. B. Bristol patent, and its purpose will be hereinafter specifically pointed out.

The galvanometer contact 38 is connected through a conductor 84 to one terminal of the coil 65, and the free terminal of that coil by means of a conductor $5 to the contact it. The contact ii is connected by means of a conductor 86 to one terminal of a small battery or other suitable source of unidirectional E. M. l. 87, and th other terminal of said source to the conduc= tor 34. The galvanometer contact is can nected through a conductor 88 to one terminal of coil II, and the free terminal that coil by means of a conductor 89, contacts 80, 8!, and a conductor 90, to one terminal of a D.-C. source at, and the other terminal of said source to the conductor.

It will be seen that, upon deflection of the galvanometer pointer 36 sufllciently for the contact 31 to engage the contact 38, a circuit will be completed from one side of the source 81 through in the network described are so selected that upon deflection of the galvanorneter in either direction by current derived from said network. flowing in the coil 3i, the supplementary current in said coil derived from the corresponding one or" the sources ill or 9! will be in such a di rection as to tend to deflect the galvanometer in the same direction with added intensity, thus supplementing the original directive effort, and tending to amplify the pressure exerted between the movable contact 37 and the stationary contact engaged thereby. The arrangement or the mechanism and the connections of the potentiometer network are such that upon energlzation of the winding 5i alone of the reversible motor til the consequent movement of the contact arm it along the slide-wire ll will be toward the terminal 32 and will tend to reduce the potential between the conductors 55 and 35; and when the winding 62 is energized alone, the movement of the arm til will be toward the terminal 63 and will tend to increase said potential.

One terminal of each of the windings 5i and 52 of the reversible motor 5b is connected to a common conductor 95 representing one side of an electric power supply. The free terminal of the winding 5i is connected by means of a conductor 96 to the contact 68 in the relay G ll, and

the cooperating contact E? to a conductor ill, forming the other side or said supply. lhe free terminal of the motor winding 52 is connected by means of a conductor 83 to the contact ll, and the coacting contact 18 to the conductor 9i. Thus, it will be seen that with the contact pairs Sit-t8 and ll-l8 in their normally closed positions, both windings of the motor 56 will be simultaneously energized, tending to stall the motor, and that with one of these contact pairs opened while the other remains closed, the motor will be energized for rotation in a corresponding direction as hereinbefore stated.

The operation of the device, as thus far set forth, may be briefly stated as follows: If the position of the contact arm 46 with respect to the slide-wire ii is such that there exists a condition of balance between the potential developed by the couple i2 and that derived from the potentiometer network, the galvanometer will stand in its un-deflected position, with the contact Ell out of engagement with either of the cooperating contacts 38 and 39; the relays 65 and i5 will be deenergized, and their respective contact pairs 6'l68 and ll-l8 closed, causing both windings point within its extended length.

6 of the motor at to be energized, and the motor consequently to remain at rest. Upon a deviation of the thermocouple potential from that derived from the slide-wire, the unbalanced condition will cause a current to flow in the galvanometer coil 3! deflecting it in a sense to close a corresponding contact, and to energize whichever one of the relays 64 and 14 will cause the motor 50 to be operated in a direction to move the contact arm 46 to a position on the slidewire where a condition of balance will be refl r P poses of discussion it may be assumed that upon an increase in the temperature measured by the thermocouple l2 the contacts of the galvanomcter 30 will be actuated in a sense to energize the coil of the relay 54, with a consequent contact action causing the motor 59 to rotate the shaft ll and parts carried thereby in a clockwise sense as seen in the drawing, and vice versa. This balancing action is characteristic of many forms of null-type instrurnents and, as it forms no part of the present invention, and, moreover, is fully set forth in the aforementioned F. 33. Bristol patent need not here be further elucidated. The function of the current flowing through the galvanometer coil 3i from the sources ill and through the contact pairs ill-ll and ilil8i, in amplifying the pressure of the galvanometer contacts, together with the timing characteristic introduced by the lagging coils or shrouds on the relay windings 65 and it is also identical with that shown in said patent and need not here be explained in further detail.

Bridge circuit and balancing mechanism Control of the valve l3 in response to deflections of the shaft ll carrying the contact arm 18 is effected by mechanism comprising the following elements in combination: Fixed to the shaft ll and rotatable therewith is a contact arm EM? engaging an arcuate slide-wire llll whereby said contact arm mayv engage said slide-wire at any Fixed to the valve-operating shaft it is a contact arm lG'Z engaging an arcuate slide-wire tilt, whereby, said last-named contact arm may engage said lastnamed slide-wire. One end of the slide-wire tilt is electrically connected to one end of the slidewire E93 by means of a conductor lilt series therewith a resistor itlh adjacent the slidewire Hi3, and an adjustable resistor ltd adjacent the slide-wire Elli. The remaining ends or" the slide-wires are similarly connected by a conductor Eill having in series therewith a resistor tilt adjacent the slide-wire i824, and an adjustable resistor its adjacent the slide-wire till.

A directional relay llil comprises a detecting coil l E l, pivoted to swing through a small angle, and having a pointer-arm l i2 carrying a doublesided contact l i 3, adapted to engage alternatively either of two stationary contacts lid and H5. The contact arms W8 and 392 are connected by conductors H6 and ill respectively to the terminals of the detecting coil ill, and the conductors tilt and till to a source of electrical energy H8, whereby the network comprising the slide wires tilt and E62 and the resistors M35, me, Hi8, and tilt forms a bridge circuit which, if unbalanced, will cause current derived from the source M8 to flow through the coil ill of the relay HG. If the current derived from the source '3 it is unidirectional in its nature, the relay till may be provided with a permanent magnet field, 'comprising a substantial equivalent of the contactmaking galvanometer 3B. As, however, it may be having in assasee desirable to have said bridge circuit energized with alternating current, the relay 9 iii is prefer ably of a form which will detect unbalance in an A.-C. bridge network, and is here shown as of the conventional wattmeter or electrodynamometer type. Juxtaposed to the movable coil ill, is a pair of stationary coils lit, electrically interconnected, and so positioned that the magnetic field produced by an electric current flowing therein will be reacted upon by current slowing in the coil ii i to produce a deflection. thereof, the sense of said deflection being dependent upon the relative instantaneous polarities of currents flowing respectively in said movable and stationary cells. The coils i it are connected in series with a suitable current-limiting resistor ifib across the source lit, whereby said coil will be energized with current of the same nature as that flowing in the bridge circuit. It will thus be apparent that an unbalanced condition of the bridge circuit, as may be established by certain relative positions of the contact arms its and lbf? with respect to their associated slide-wires, will result in a deflection oi the coil iii, and that electrical engagement of the movable contact its will be effected with stationary contact M6 or iil, according to the sense of the unbalance.

The stationary contact lid of the relay M9 is connected by means of a conductor 52! to the terminal 25 of the motor 2:2 and the contact lib of said relay by means of a conductor H22 to the terminal 26 of said motor. The. movable contact lit; is connected by means of a flexible lead its to one side, and the terminal 2'3 of the motor Ed by means of a conductor ltd to the other side, of the source H8. it will be seen that the combination of the motor 28 and the relay lit provides means whereby the arm it? may be moved in response to unbalance conditions of the bridge network, so that by suitably proportioning the several resistance units in the network, and selecting polarities, there is provided a follow-up system, whereby a movement of the contact arm use due to the potentiometer-circuitbalancing action of the motor at will cause a corresponding positioning action of the arm 362, and consequently of the valve E3, to be effected by the motor 263*. The selection of polarities is made such that, upon a movement'of the contact-arm ltd toward the right, as seen in the drawing, in response to an increase in the measured temperature, the contact arm its will also be moved toward the right, and the valve'ifi operated in a sense to effect closing thereof. Thus,

with the resistors ltd, iiltl, i538, and W9 included in circuit with the branches of the slide-wires Bill and MS, as divided by the contact arms Hill, and M2, the valve l3 will have a definite position corresponding to each selected position of the shaft ll and elements carried thereby. It will further be obvious that, while the motor 20 has been shown as operated from the same source of supply as the bridge network, there exists no need for interconnection of these circuits; and, if found expedient, the motor and the bridge may be effectively energized from independent sources.

Anticipating relay A relay 930 having an actuating coll 531 is provided with two sets of normally open contacts I32 and 533, and one set of normally closed contacts i3 3. One side of the winding l3i is connected to one side of the contacts I32, and by a conductor I36 to the auxiliary contact 83 of the relay 16. The other side of the winding l3l is connected to the conductor as. The free side of sthe contacts l32 is connected to the conductor 9t, and thereby to the contact 68 in the relay 65.

The contacts 538 are connected to the two ends 5 of the resistor H33, and the contacts H336 to the two ends of the resistor ltd, whereby either of said resistors will be short-circulted by the closure of the associated contacts, and one or other of said resistors will at all times be closed, depending upon whether the winding 83E of the relay lllt is in an energized or a de-energized condition.

The operation of the auxiliary relay ifill and associated connections is as follows: It has already been pointed out that, with resistors its and 3% both included in the bridge network of which they form a part, the valve iii will tend to assume positions corresponding to selected pcsltlons of the shaft il, so that for each value of there will be a definite position of said valve. It

will also be seen that, with the contacts ltd of the relay iSB closed, as shown in the drawing, corresponding to a de=energized condition of said relay, the resistor its will be short-circuited, thus distributing any balance that may have been established in the bridge network, and requiring that, without any change in the position of the contact-arm Hill, the contact-arm it shall assume another than its original balance position with respect to the arm tilt in order to restore the balance in the network. It will further be apparent that the short circuiting of the resistor we will disturb the proportionality of the bridge network in such a sense that restoration ofthe balance will require movement of the arm H32 toward the right, as shown in the drawing, or in a direction corresponding to a closing action of the valve is. In a similar manner, closing of the contacts 933, corresponding to an energized condition of the relay 83d, will shortcircuit the resistor ltd, unbalancing the bridge network, and for restoration of the balance, requiring that the arm lllZbe moved toward the left, as seen in the drawing, and the valve it opened to a proportionate extent.

Assuming that the relay lat has been resting in its de-energized condition, with contacts E32 and 838 open and contacts id i closed, and that the temperature as measured; by the thermocouple i2 should fall, action of the galvanometer 39 will close the contacts 37t9, and energize the wind= ing 16 of the relay it, establishing a, contact condition tending to deflect the pointer 63 to the left on the scale so, and also toshift the contact arm Hit in a sense to bring about through normal unbalance of the bridge network a corresponding opening action of the valve it. At the same time, the action of the armature it of the relay ill will cause the contacts ls-t3 to be brought into engagement, providing a circuit, whereby current from the conductor 9i may pass through said last-named contacts and the conductor 536 to the winding it! of the relay 130 and thence to the conductor Q5, completing a circuit to energize said last-named relay, and close both the contacts i32 and H3. The closing of the contacts use, as hereinbefore pointed out, will result in an immediate unbalance of the bridge network in which the relay H0 is included, causing the motor 23 to be energized in a sense to open the valve is in anticipation of the control influence subsequently to be derived from the movement of the contact-arm H80 in the normal course of balancing the potentiometer temperature as measured by the thermocouple l2,

circuit. Closing of the contacts I32 provides a path from the conductor I36 to the conductor Q5, and through the contacts 61-58 of the relay '64 to the conductor 91, so that once the relay i3 is energized it will remain locked in its energized position by virtue of current flowing through said path until the conductor 96 is disconnected from the conductor 91 by opening of the contacts 61-68. Thus, the biasapp1ied to the valve I3 will be maintained so long as the relay I30 remains energized, which will be until the first succeeding impulse from the galvanometer 30 indicating an. increasing of the measured temperature. This impulse, closing the contacts 31-48, and energizing the winding 65 of the relay 54, will cause the contacts 51-68 to be separated, which action, besides afiecting the performance of the motor 50 as hereinbefore set forth, will cause the winding till of the relay E30 to be tie-energized, opening the contacts I32 and lit, and closing the contacts E34, which will immediately bias the valve l3 in a closing sense and in anticipation of an influence subsequently to be derived from movement of the arm Hid along the slide-wire til i.

For purposes of simplicity in following the actions of the various elements in the mechanism under conditions of rising or falling temperature, reference may be had to the following table, in which several elements of the mechanism are identified in the middle column, and their respectiev states corresponding to high, and to low, temperature are indicated in the left-hand and right-hand columns respectively:

1 -gg g Element Temperature Low clockwise Galv. Coil 3i counter-clockwise closed contacts 37-38 opened opened contacts 37-39 closed energized relay coil 65 tie-energized dc-encrgizcd relay coil 75 energized opened contacts 67-68 closed closed contacts 77-78 opened opened contacts 70-71 closed closed contacts 80-81 opened opened contacts 78-83 closed (lo-energized winding 51 energized energized winding 52 tie-energized clockwise shaft 47 counter-clockwise closed contacts 113-114 opened opened contacts ll3-ii5 closed vncrgized winding 21 de-energized (la-energized winding 22 energized countcr-clockw isc shaft 19 clockwise closing valve 13 (normal) opening lc-cncrgi'zcd relay coil 131 energized opcucrl contacts 133 closed clos d contacts 134 opened in circuit resistor 106 shorted shorted resistor 109 in circuit closing valve 13 (anticipatory) opening There has thus been provided means whereby there are combined the advantageous features of the so-called thermostatic control, in which a change of temperature in a given direction results in a substantially immediate response of a valve controlling a temperature-affecting agent, and the floating control, wherein said valve tends to be positioned to a degree of opening corresponding to the actual value of the measured temperature. As is well-known to those versed in the art of regulation, the closest possible automatic approach to the ideal control is found in a properly proportioned combination of these two forms of operation. If the resistance values of the resistors i516 and H39 are manually reduced to zero the anticipating effect of the relay E30 7 will be nullified; while if these values are abnormally increased a condition of instability will be introduced. These resistors may be readily ad- Justed manually to optimum values governed by particular operating conditions whereby there will result an intermediate condition in which inherent backlash in the basic control system will be neutralized without at the same time introducing an unstable condition, whereby a substantially straight-line control will be effected.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim:

1. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-affecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the influence of said sensitive means to assume different positions to restore a balanced condition in said electrical means, said positions being representative of the magnitudes of said. condition, means operatively coupling said measuring instrument and said motor and adapted to cause said motor to move said valve toward positions corresponding to those assumed by said member of said instrument, and further means directly and substantially instantaneously responsive to said sensitive means independently of the position of said member for modifying the coupling between said instrument and motor and in a sense to anticipate the influence normally transmitted through said coupling means.

2. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-affecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the infiuence of said sensitive means to assume different positions to restore a balanced condition in said electrical means, said positions being representative of the magnitudes of said condition, means operatively coupling said measuring instrument and said motor and including a bridge network, resistance means actuated by said instrument to affect the balance of said network, other resistance means actuated by said valve motor to affect the balance of said network, in strumentalities in said network and sensitive to unbalance conditions in the same and adapted to cause said motor to actuate said other resistance means in a sense to restore electrical balance in said network, and further resistance means in said network and means responsive to said sensitive means independently of the position of said member for modifying said last-named resistance means to affect the electrical balance in the same sense as the effect due to said first resistance means as actuated by said instrument in response to said sensitive means.

3. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-affecting agent, means sensitive to changes in said condition, a measuring instrument having a member adapted to assume different positions representative oi. the magnitudes of said condition and in response to the influence of said sensitive means, a bridge it network comprising a first resistance element adapted to be varied to affect the balance of said network in accordance with the position of said member and a second resistance element adapted to be varied to afiect the balance of said network by said valve-actuating motor, relay means in said network adapted to respond to unbalance conditions in the same to command the operation of said motor, whereby said valve will nor= mally be positioned in accordance with the position assumed by said member, further resistance elements associated with said network, and contact means adapted to cause said further elements to be included into or excluded from said network, in response and definite correspondence to actions of said sensitive means, to aifect the balance conditions of said network in the same sense as said balance conditions will be affected by said first resistance element, and thereby to cause said motor to tend to position said valve in anticipation of the influence of variation of said first resistance element.

4. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-affecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in. said condition and a member adapted under the iniiuence of said sensitive means to assume difierent positions to restore a balanced condition in said electrical means, said positions being representative of the magnitudes of said condition, a

bridge network comprising a first resistance ele= merit adapted to be varied to afiect the balance of said network in accordance with the position of said member and a second resistance element adapted to be varied to affect the balance of said network by said valve-actuating motor, relay means in said network adapted to respond to unbalance conditions in the same to command the operation of said motor, whereby said valve will normally be positioned in accordance with the position assumed by said member, means adapted to bias said network on either side of a balance condition whereby its balance may be afiected without varying either said first or said second resistance element, means subject to said sensitive means independently of the position of said member to actuate said biasing means in one sense upon a change in. said condition in a given direction, and to actuate said biasing means in a reverse sense upon a change in an opposite direction.

5. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-affecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the influence and said motor and adapted to cause said motorto move said valve toward positions corresponding to those assumed by said member of said instrument, and further means directly and substantially instantaneously responsive'to said sensitive means on a first response only of said sensitive means to a change in said condition in a given direction subsequent to a change in the opposite direction, for modifying the coupling beaccuses i2 tween said instrument and motor and in a sense to anticipate the influence normally transmitted through said coupling means.

6. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-afiecting agent, means sensitive to changes in said condition, a measuring instrument having a member adapted to assume different positions representative of the magnitudes of said condition and in response to the influence of said sensitive means, a bridge network comprising a first resistance element adapted to be varied to affect the balance of said network in accordance with the position of said member and a second resistance'eiement adapted to be varied to aiiect the balance of said network by said valve-actuating motor, relay means in said network adapted to respond to unbalance conditions inthe same to command the operation of said motor, whereby said valve will normally be positioned in accordance with the position assumed by said member, further resistance elements associated with said network, a relay, contacts on said relay, a locking circuit for said relay adapted to be completed by said contacts and to be opened by said sensitive means, means actuated by said sensitive means for energizing said relay, circuit controlling means actuated by said relay and adapted to cause said further re,- sistance elements to be included in or excluded from said network to affect the balance conditions in the same sense as said balance conditions will be affected by said first resistance element, and thereby to cause said motor to tend to position said valve in anticipation of the influence of variation of said first resistance element.

7. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-affecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the infiuence of said sensitive means to assume different positions to restore a balanced condition in said electrical means, said positions being representative of the magnitudes of said condition, a bridge network comprising a first resistance element adapted to be varied to affect the balance of said network in accordance with the position of said member and a second resistance element adapted to be varied to affect the balance of said network by said valve-actuating motor, relay means in said network adapted to respond to unbalance conditions in the same to command the operation of said motor, whereby said valve will normally be positioned in accordance with the position assumed by said member, means adapted to biassaid network on either side of a balance condition whereby its balance may be aiiected without varying either said first or said second resistance element, means subject to said sensitive means to actuate said biasing means in one sense upon a first response only oi said sensitive means to a change of said condition in a given direction, and to actuate said biasing means in an opposite sense upon the first subsequent response of said sensitive means to'a change of said condition in an opposite direction:

'8. In a system for automatically regulating a condition, a motor adapted to actuate a valve for controlling a condition-afiecting agent, electric means sensitive to change in said condition, a galvanometer responsive to said electric means,

. 13 I a potentiometer network including said galvanometer and said sensitive means, mechanical means adapted to balance said potentiometer network, relay means actuated by said galvanometer for controlling said balancing means, a bridge network, a first variable resistance element in said bridge network and adapted to be varied by said potentiometer balancing means whereby the balance of said bridge may be affected, a second variable resistance element in said bridge network and adapted to be varied by said valve motor whereby the balance of said bridge may be aiiected, relay means in said bridge network adapted to respond to unbalance tion of said motor, whereby said valve will normally be positioned in accordance with the position assumed by said potentiometer-balancing means, further resistance elements associated with said network, and contact means adapted to cooperate individually with said further elements to cause the same to be included in or excluded from said bridge network, electrical means for actuating said contact means and a circuit for said electrical means, circuit-affecting means included in said galvanometer-actuated relay means for selectively controlling saidcontact means in accordance with the sense of change in said condition as detected by said galvanometer to modify the balance of, said bridge network by the inclusion or exclusion of said last-named resistance elements, and thereby to cause said motor to tend to position said valve in anticipation of the influence of variation of said first resistance element.

9. In a system for automaticaly affecting a condition, a motor adapted to actuate an element for controlling said condition, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the influence oi said sensitive means to assume different positions to restore a balanced condition in said electrical means, said positions being representative of the magnitudes of said condition,, means operatively coupling said measuring instrument and said motor for causing said motor to move said element in accordance with the operation of said member, and further means directly and substantially instantaneously responsive to said sensitive means independently of the position of said member for causing said motor to impart to said element a movement anticipatory oi the innuence normally transmitted through said coupling means.

10. In a system for automatically regulating a condition, a motor adapted to actuate an element ibr controlling a condition-aflecting agent,

, means sensitive to changes in said condition,

a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the influence of said sensitive means to assume diflerent positions to restore a balanced condition in said electrical means, said positions being representative oi the magnitudes oi! said condition. means operatively coupling said measuring instrument and said motor and adapted to cause said motor to move said element toward positions corresponding to those assumed by said member of said instrument, and iurther means directly and substantially instantaneously responsive to said sensitive means independently of the position of said member for modifying the coupling between said instrument and motor and in a sense to anticipate the influence normally transmitted through said coupling means.

11. In a system for automatically regulating a condition, a motor adapted to actuate an element for controlling a condition-aflecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the influence of said sensitive means to assume different positions to restore a balanced condition in said electrical means, said positions being representative of the magnitudes of said condition, means operatively coupling said measuring -instrument and said motor and including a bridge network, resistance means actuated by said instrument to afiect the balance of said notwork, other resistance means actuated by said motor to affect the balance of said network, instrumentalities in said network and sensitive to unbalance conditions in the same and adapted to cause said motor to actuate said other resistance means in a sense to restore electrical balance in said network, and further resistance means in said network and means responsive to said sensitive means independently of the position of said member for modifying said lastnamed resistance means to afiect the electrical balance in the same sense as the effect due to said first resistance means as actuated by said instrument in response to said sensitive means.

12. In a system for automatically regulating a condition, a motor adapted to actuate an element for controlling a condition-aflecting agent, means sensitive to changes in said condition, a measuring instrument comprising electrical means adapted to be unbalanced by changes in said condition and a member adapted under the influence of said sensitive means to assume different positions to restore a balanced condition in said electrical means, said positions being representative oi the magnitudes of said condition, means operatively coupling said measuring instrument and said motor and adapted to cause said motor to move said element toward positions corresponding to those assumed by said member of said instrument, and further means directly and substantially instantaneously responsive to said sensitive means on a first response only of said sensitive means to a change in said condition in a given direction subsequent to a change in the opposite direction, for modifying the coupling between said instrument and motor and in I a sense to anticipate the influence normally transmitted through said coupling means.

GEORGE E. VAN VESSEM.

REFERENCES CITED The following references are 0! record in the flle 01' this patent:

UNITED STATES PATENTS 

